Rotary actuators are used in a variety of applications where it is desired to effect movement of a rotary fashion about a center-point. Such actuators are used, for example, to open and close valves, turn switches, operate steering mechanisms, etc. Moreover, rotary actuators are known and often used in practice with a platform of a special motor vehicle for lifting a person using a vertical mast lift or boom to work at high places, over and around electrical and telephone lines, duct work and trees during construction, to make repairs, and/or to do maintenance work.
The actuator may be of the double-action type, as in this case, wherein fluid, either hydraulic or pneumatic, is used to displace a piston in an oscillating manner in a chamber to effect rotation of an axial rod or shaft in a clockwise and counterclockwise direction, depending on movement of the attached piston. More specifically, a rotary helical grooved or splined actuator typically uses a cylindrical body with an elongated rotary output shaft extending coaxially within the body, with an end portion of the shaft providing the rotational drive output. An elongated, annular piston sleeve has a splined portion to engage between and cooperate with corresponding splines on an interior of the cylindrical body and an exterior of the output shaft. The piston sleeve is reciprocally mounted within the body and has a piston head portion for the application of fluid pressure to one or the other opposing sides to produce axial movement of the piston sleeve in the cylindrical body and along the output shaft.
In use, as the piston sleeve reciprocates linearly in the axial direction within the body, the outer helical splines of the piston sleeve engage helical splines of the body to cause rotation of the piston sleeve. As a result, linear and rotational movement of the piston sleeve is transmitted through the inner helical splines of the piston sleeve to the helical splines of the shaft that causes the shaft to rotate.
Accurate and efficient cutting of the mating helical grooves or splines across the interiors and exteriors of the piston sleeve, cylindrical body and axial shaft or rod, accordingly, can be difficult and expensive. As an alternative, U.S. Pat. No. 6,966,249 describes a rotary actuator using pins to engage the splines. Moreover, a first set of pins are positioned via passages through the piston sleeve to engage the splines on the exterior of the axial shaft, and a second set of pins are fixedly installed through holes in the cylindrical body to engage the helical splines of the piston. In operation, the first pins, fixed to the piston, are inserted in the slant grooves of the axial shaft, and the second pins fixed to the cylindrical body are inserted in the slant grooves or splines of the piston. Thus, with this coupling structure, when the piston moves, it rotates with respect to the cylindrical body and the axial rod or shaft is rotated with respect to the piston.
This approach is less efficient and more unreliable than the instant invention in that the through-hole openings in the cylinder body and reciprocating piston used to accommodate the first and second sets of pins, act as points of fatigue and ultimately leakage of hydraulic or pneumatic fluid; leading to premature failure of the actuator, particularly when used with heavy loads.
Korean Publication No. 2005-0018741 shows an alternative design eliminating the through-holes in the cylinder body, using instead bearings to travel along linear grooves aligned with the axis of the axial rod. However, this design is inferior to the instant invention, in that the rotation of the axial rod is simply subject to the slant angle of the splines or grooves of the axial rod (versus the combined helical angles of the splines of the axial rod and piston). Further, Korean Patent Application No. 2005-0018743 includes through-holes in the piston for a second set of pass-through bearings engaging both the linear grooves of the cylindrical body and helical grooves of the piston rod. This arrangement is prone to uneven wear of the bearings as each bearing is forced to rotate in a different direction caused by contact against the corresponding linear and helical grooved surfaces.
There is a need, therefore, for a rotary actuator capable of effectively and more efficiently supporting and rotating a heavy load repeatedly, without failure, in a confined and compact space. The object of the present invention is to solve the problems associated with the known arrangements at the least possible expense, so that large-scale production of an effective, efficient and durable actuator can be manufactured and maintained at an acceptable cost. Regarding the instant invention, the rotary actuator can be used to support a heavy structure such as a platform or a lifting arm. It can be installed easily in a small and/or confined space, being durable and efficient, without points susceptible to fatigue, leakage, undue wear per cycle, and other deficiencies prone with the existing actuators described above.